There is known a process for obtaining propylene oxide by reacting an organic peroxide, for example, cumene hydroperoxide with propylene in the presence of a epoxidation catalyst.
In this case, oxygen-containing compound such as water, methanol, acetaldehyde, acetone and propionaldehyde, hydrocarbons and the like are produced as by-products in addition to propylene oxide as a target product. Therefore, a purification step for separating and removing these impurities from propylene oxide to obtain high purity propylene oxide become necessary. Purification processes of propylene oxide are disclosed in U.S. Pat. No. 5,139,622, European Patent 1498414 A or the like.
In addition, it is publicly known to subject to extractive distillation using a hydrocarbon as an extractant in purification of propylene oxide. For example, U.S. Pat. No. 3,843,488 discloses that an alkane such as octane is effective for removing hydrocarbons having 6 carbon atoms as impurities. Further, U.S. Pat. No. 3,607,669 discloses that an alkane such as octane is effective for removal of water. Furthermore, U.S. Pat. No. 5,133,839 discloses that a hydrocarbon such as octane is effective for removal of impurities such as methanol, propionaldehyde and acetone.
However, in the conventional techniques, any concrete method for removing methyl formate at high level is not disclosed. There was a problem that this methyl formate in propylene oxide markedly deteriorated a quality of propylene oxide used as a raw material for various chemical products.